Logical biMOS gate circuit having low power dissipation

ABSTRACT

A logical gate circuit includes an emitter-grounded switching transistor and a pull-up circuit connected to a collector of the switching transistor. The switching transistor is cut OFF when an input signal has a high level and is turned ON when the input signal has a low level. A control MIS transistor is connected to a base of the switching transistor and is turned ON and OFF in response to respective low and high levels, of the output terminal of the switching transistor. An input transistor is connected in series with the control MIS transistor and is turned ON and OFF when the input signal is high and low, respectively. Thus, the logical gate circuit allows current to flow only during a transient signal period.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a logical gate circuit. More particularly, it relates to a logical gate circuit which provides a bipolar transistor at the output stage, such as a TTL gate circuit.

2. Description of the Related Art

In a conventional logical gate circuit using a bipolar transistor, for example a TTL gate circuit, a bipolar transistor having a high drive capacity, and in particular, a bipolar transistor having a vertical construction, is suitable for rapidly switching a large current. As the TTL circuit provides an emitter grounded type inverter using such a bipolar transistor at the output stage, high speed and large current switching capacity are possible and a capacitive load can be used.

However, such a conventional logical gate circuit has some drawbacks, for example, when the inverter transistor at the output stage is ON, the base current and the collector current continuously flow, resulting in high power dissipation.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a logical gate circuit having a low power dissipation and a high driving capacity.

Another object of the present invention is to provide a logical gate circuit in which the current flows only when the logical gate circuit is in a transient state.

According to the present invention, to solve the above problems, a logical gate circuit is provided comprising an emitter grounded type switching transistor, an active load circuit connected to a collector of the switching transistor, which is cut off when an input signal is at a first level and is made on when that input signal is at a second level and control MIS transistor means connected in series with input MIS transistor means in a base circuit of the switching transistor. The control MIS transistor is made ON or OFF in response to the ON and OFF of the switching transistor. The input MIS transistor means is made ON when the input signal is at the first level.

Preferably, the logical gate circuit comprises an NPN transistor and a PNP transistor, each having a collector connected to a common output terminal and each having an emitter connected to a first and a second power source, respectively, first and second N channel MIS transistor means connected in series between the base of the NPN transistor and the second power source, and first and second PNP transistor means connected in series between the base of the PNP transistor and the first power source. The first N channel MIS transistor means and the first P channel MIS transistor means are made ON and OFF in response to an output signal and the second N channel MIS transistor means and the second P channel MIS transistor means are made ON and OFF in response to the input signal.

According to the present invention, by using the above-mentioned means, after the emitter grounded type switching transistor at the output stage is placed in an OFF state, the base current of the switching transistor is cut off. Therefore, after the transient operation, the switching transistor again enters a cut off state, so that the power dissipation in the steady state can be reduced to almost zero.

Further features and advantages of the present invention will be apparent from the ensuing description with reference to the accompanying drawings to which, however, the scope of the invention is in no way limited.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the principle of the logical gate circuit of one embodiment of the present invention;

FIG. 2 is a timing diagram for explaining the operation of the circuit shown in FIG. 3;

FIG. 3 is a circuit diagram of an embodiment of the present invention;

FIGS. 4 and 5 are circuit diagrams of a modified embodiment of the circuit shown in FIG. 3;

FIG. 6 is a circuit diagram of another embodiment of the present invention;

FIG. 7 is circuit diagram of a modified embodiment of the circuit shown in FIG. 6;

FIGS. 8 to 10 are circuit diagrams of further embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the embodiment of the present invention will be explained with reference to the drawings. FIG. 1 shows the principle of the logical gate circuit of one embodiment of the present invention. The circuit shown in FIG. 1 provides a bipolar transistor, namely, an inverter transistor Q₁ having an emitter connected to a low voltage terminal V_(L) of the power source, that is, an emitter grounded transistor, a pull up circuit C connected between the collector of the inverter transistor Q₁ and a high voltage terminal V_(H) of the power source, and switching circuits A and B connected between the base of the transistor Q₁ and the high voltage terminal V_(H). The pull up circuit C is controlled by an input signal I and enters an ON state when the input signal IN becomes low level. The switching circuit A is also controlled by the input signal IN, but enters an ON state when the input signal IN becomes high level. The switching circuit B is controlled by the collector voltage of the transistor Q₁, that is, the output signal OUT, and the switching circuit B enters in an ON state when the collector voltage becomes high level. The pull up circuit C and switching circuits A and B are formed by a switching elements having a high input impedance, for example, MIS type transistors. Further, the switching circuits A and B are connected in series, and thus it is possible to change the order thereof.

The operation of the circuit shown in FIG. 1 will be explained with reference to FIG. 2. When the input signal IN is at a low level, the pull up circuit C is in an ON state, and the output signal OUT is at a high level. Therefore, the switching circuit B is in an ON state. However, when the switching circuit A is in the cut off state, then the base current of the transistor Q₁ is not supplied, so that the transistor Q₁ is in an OFF state. When the input signal IN is changed from low level to high level, the switching element A enters an ON state. Then, the base current is supplied via the switching elements A and B from the high voltage terminal V_(H) to the transistor Q₁, so that the transistor Q₁ enters an ON state. At this time, the pull up circuit C is in a cut off state, so that the output signal OUT is changed from high level to low level. When the output signal OUT is changed to low level, the switching circuit B enters a cut off state and the base current of the transistor Q₁ is cut off, then the transistor Q₁ enters an OFF state. At this time, the pull up circuit C is in the cut off state, therefore, if the transistor Q₁ enters an OFF state, the output OUT is held at a low level. As shown in FIG. 2, the base current I_(B) of the transistor Q₁ flows transistently when the transistor Q₁ is changed to the ON state, and does not flow after the output signal OUT becomes low level at a steady state. Further, during the time that the output signal OUT is at the low level, the pull up circuit C is also in a cut off state, and the current does not flow in the output stage including the pull up circuit C and the transistor Q₁.

Next, when the input signal IN changes from high level to low level, the pull up circuit C becomes ON and the output signal OUT is raised to a high level. At this time, as mentioned above, the transistor Q₁ is in a cut off state immediately after the output signal OUT is changed from high level to low level, then, even when the input signal IN is then inverted and the output signal OUT changed from low level to high level, a rush current does not occur and a high speed switching is carried out. Further, even when the output signal OUT is in a high level at a steady state, the switching element A is placed in a cut off state by the input signal IN, and the transistor Q₁ is in a completely cut off state, therefore, no current flows in the output stage.

FIG. 3 shows a logical gate circuit according to another embodiment, which utilizes the circuit shown in FIG. 1. The circuit shown in FIG. 3 provides an emitter grounded NPN switching transistor Q₁. In FIG. 3, a P-channel MOS transistor Q₂, used as the pull up circuit C, is an enhancement type transistor, an N-channel MOS transistor O₃, used as the switching circuit A, is also an enhancement type transistor, and an N-channel MOS transistor Q₄, used as the switching circuit A, may be a depletion or enhancement type transistor. When a depletion type transistor is used, a sufficient low level can be obtained at the output OUT, but when an enhancement type transistor is used, the low level obtained at the output OUT is somewhat high. As only the base current of the transistor Q₁ flows in the transistors Q₃ and Q₄, the current capacity of the transistors Q₃ and Q₄ may be small.

In the circuit shown in FIG. 3, when the input IN is in a high level state, the transistor Q₁ is OFF, the transistor Q₃ is ON, and the transistor Q₄ is OFF, because the output OUT is at a low level as mentioned above. Therefore, the base current and the collector current of the transistor Q₁ are both cut off. Further, when the input signal IN is in a low level state, the transistor Q₃ is in an OFF state, and the transistor Q₁ is also in an OFF state. The transistor Q₂ is in an ON state and the output signal OUT is held at a high level. Therefore, in this case also, both the base and collector of the transistor Q₁ are cut off. Further, the impedance element Z is provided to sufficiently discharge the charges in the base of the transistor Q and completely cut off the transistor Q₁ when the input signal IN becomes low level, or when the output signal OUT becomes low level and the transistor Q₃ or Q₄ is cut off.

In the circuit shown in FIG. 3, the transistors Q₂ and Q₃ are preferably enhancement type, because these transistors are made ON and OFF in accordance with the input signal IN. The low level V_(OL) in the output is as follows:

    V.sub.OL =V.sub.BE (Q.sub.1)+V.sub.th (Q.sub.4)

Then, to obtain a sufficiently low V_(OL), it is preferable that the Q₄ transistor be the depletion type. This is because the value of V_(th) (Q₄) will be negative. Thus, this circuit is suitable to lower the value of V_(OL). Further, the input of the next stage gate to be connected to the output OUT, preferably has a high impedance, such as an MIS transistor gate terminal, because, the transistors Q₁ and Q₂ are both in a cut off state when in the steady state. Furthermore, the size of the MOS transistors Q₃ and Q₄ may be small, because these transistors have only to supply a small base current to the transistor Q₁.

FIG. 4 shows a modified embodiment of the circuit shown in FIG. 3. In FIG. 4, n transistors Q_(2a) , Q_(2b) . . . , Q_(2n) are connected in parallel as the pull up circuit, and n transistors Q_(3a) , Q_(3b) . . . , Q_(3n) are connected in series as the switching circuit A. Inputs A₁ , A₂ , . . . , A_(n) are connected to the gates of the transistor Q_(2a) , . . . , Q_(2n) and the transistor Q_(3a) , . . . , Q_(3n) as shown in FIG. 4. The circuit shown in FIG. 4 functions as a NAND circuit, that is, the output OUT is expressed as:

    OUT=AHD 1 A.sub.2 . . . An

FIG. 5 shows another modified embodiment of the circuit shown in FIG. 3. In FIG. 5, n transistors Q_(2A) , Q_(2B) , . . . , Q_(2N) are connected in series as the pull up circuit, and n transistors Q_(3A) , Q_(3B) , . . . , Q_(3N) are connected in parallel as the switching circuit A. Inputs A₁ , A₂ , . . . , A_(n) are connected to the gates of the transistors Q_(2A) , . . . , Q_(2N) and the transistors Q_(3A) , . . . , Q_(3N) as shown in FIG. 5. The circuit shown in FIG. 5 functions as a NOR circuit, that is, the output OUT is expressed as:

    OUT=A.sub.1 +A.sub.2 + . . . +AN

FIG. 6 shows a logical gate circuit according to a further embodiment of the present invention which utilizes the circuit shown in FIG. 1. In the circuit shown in FIG. 6, the inverter transistor Q₁ in FIG. 1 is replaced by a PNP type switching transistor Q₅ , the pull up circuit C is replaced by an N channel MOS transistor Q₆ , and the switching transistor A and B are replaced by P channel MOS transistors, Q₇ and Q₈ , respectively.

FIG. 7 shows a modified embodiment of the circuit shown in FIG. 3. In FIG. 7, n transistors Q_(6a) , Q_(6b) , . . . , Q_(6n) are connected in parallel as the pull down circuit, and n transistors Q_(7a) , Q_(7b) , . . . , Q_(7n) are connected in series as the switching transistor circuit A. Inputs A₁ , A₂ , . . . A_(n) are connected to the gates of the transistors Q_(6a) , . . . Q_(6n) and the transistors Q_(7a) , . . . , Q_(7n) , as shown in FIG. 7. The circuit shown in FIG. 7 functions as a NOR circuit, that is, the output OUT is expressed as:

    OUT=A.sub.1 +A.sub.2 + . . . +AN

FIG. 8 shows a complemental type logical gate circuit according to a still further embodiment of the present invention. This circuit is formed by combining the circuits of FIG. 3 and 6. The circuit shown in FIG. 8 includes NPN transistor Q₁ and PNP transistor Q₅ , the collectors of which are connected to each other and the emitters of which are connected to the low voltage terminal V_(L) or the high voltage terminal V_(H) , respectively; N channel MOS transistors Q₃ and Q₄ connected in series between the base of the transistor Q₁ and the high voltage terminal V_(H) ; P channel MOS transistor Q₇ and Q₈ connected in series between the base of the transistor Q₅ and the low voltage terminal V_(L) ; and impedance elements Z₁ and Z₂ respectively connected between the base of the transistors Q₁ or Q₅ and the low voltage terminal V_(L) or the high voltage terminal V_(H). The gates of the transistors Q₃ and Q₇ are connected to the input terminal and the gates of the transistors Q₄ and Q₈ are connected to the output terminal.

In the circuit shown in FIG. 8, when the input signal IN changes from high level to low level at the time when the output signal OUT is low level, the transistor Q₇ enters the ON state. The transistor Q₈ is in an ON state and when the output signal OUT is low level. Thus, the base potential of the transistor Q₅ is lowered so that the transistor Q₅ is placed in an ON state. Then the output signal OUT is raised to a high level and the transistor Q₈ is cut off, which cut, off the base current of the transistor Q₅. Therefore, after the output signal OUT is placed in a high level steady state, the transistor Q₅ is cut off, and thus a steady current does not flow in the output stage. Further, in this case, when the input signal IN is at a low level, then the transistor Q₃ is cut off and the transistor Q₁ is also cut off. When the input signal IN changes from low level to high level, a similar operation is carried out. In each case, it is clear that the current flows in the transient state but does not flow in the steady state. Further, in the circuit shown in FIG. 8, as the output stage is formed by the complementary bipolar transistors, the driveability is increased by a signal of either polarity, and thus the operation speed can be increased. Further, by using a complementary type circuit, the noise margin can be improved.

FIG. 9 shows a logical gate circuit as a further embodiment of the present invention. In the circuit shown in FIG. 9, a combination of P channel MOS transistor Q₁₀ and NPN type transistor Q₉ is used in place of the P channel MOS transistor Q₂ in the circuit shown in FIG. 3. The other portions are same as the circuit shown in FIG. 3, and same reference numericals are used as in FIG. 3. In the circuit shown in FIG. 9, the output stage is also formed by bipolar transistors, so that the driveability is increased and a high speed operation can be carried out.

FIG. 10 shows a logical gate circuit as a still further embodiment of the present invention. In the circuit shown in FIG. 10, the N channel MOS transistor Q₆ in the circuit shown in FIG. 6 is replaced by a combination of an N channel MOS transistor Q₁₂ and a PNP transistor Q₁₁. The other portions of this circuit are the same as the circuit shown in FIG. 6. In this circuit, the output stage is also formed by the bipolar transistor, so that the driveability is increased and a high speed operation can be carried out.

As mentioned above, according to the present invention, a bipolar transistor having a large driving ability can be used and the power dissipation in the steady state can be reduced to zero, so that a logical gate circuit having low power dissipation and high speed operation can be realized. Further, in the present invention, a depletion-type MOS transistor Q₄ can be used, with an emitter-grounded bipolar transistor Q₁ in an amplifier or inverter so that the low level of the output OUT can be sufficiently lowered. 

We claim:
 1. A logical gate circuit comprising:first and second power sources for supplying first and second levels, respectively; an input terminal for receiving an input signal having one of the first and second levels; an output terminal for providing an output signal having one of the first and second levels; a switching transistor, having an emitter operatively connected to said second power source, having a collector operatively connected to said output terminal and having a base, said output terminal outputting the output signal with the second level in response to said switching transistor having an ON state; an active load circuit, operatively connected between said first power source and the collector of said switching transistor and to said input terminal, said active load circuit being turned OFF in response to the input signal having the first level and being turned ON in response to the input signal having the second level, the output signal having the first level when said active load circuit is ON; control transistor means, operatively connected to the base of said switching transistor having a control terminal connected (and) to said output terminal, for controlling said switching transistor in response to the output signal, said control transistor means turning ON and OFF in response to the output signal having the first level and the second level, respectively; and input transistor means, operatively connected between said first power source and said control transistor means and operatively connected to said input terminal, for controlling said switching transistor in response to the input signal, said input transistor means turning ON and OFF in response to the input signal having the first level and the second level, respectively, said switching transistor being turned ON only when said control and input transistor means are ON and provide a base current thereto.
 2. A logical gate circuit, comprising:a first power source for supplying a first level; a second power source for supplying a second level lower than the first level; an input terminal for receiving an input signal having one of the first and second levels; an output terminal for providing an output signal having one of the first and second levels; an NPN type bipolar transistor, having an emitter operatively connected to said second power source, having a collector operatively connected to said output terminal and having a base, said output terminal outputting the output signal with the second level in response to said NPN type bipolar transistor having an ON state; a P-channel MIS transistor having a source operatively connected to said first power source, a drain operatively connected to said output terminal and a gate operatively connected to said input terminal, said P-channel MIS transistor being turned OFF in response to the input signal having the first level and being turned ON in response to the input signal having the second level, the output signal having the first level when said P-channel MIS transistor is ON; a first N-channel MIS transistor having a source operatively connected to the base of said switching transistor and a gate operatively connected to said output terminal, for controlling said NPN type bipolar transistor in response to the output signal, said first N-channel MIS transistor turning ON and OFF in response to the output signal having the first level and the second level, respectively; and a second N-channel MIS transistor having a source connected to the drain of said first N-channel MIS transistor, a gate operatively connected to said input terminal and a drain operatively connected to said first power source, for controlling said NPN type bipolar transistor in response to the input signal, said second N-channel MIS transistor turning ON and OFF in response to the input signal having the first level and the second level, respectively, said NPN type bipolar transistor being turned ON only when said first and second N-channel MIS transistors are ON and provide a base current thereto.
 3. A logical gate circuit according to claim 2, further comprising an NPN transistor having a collector operatively connected to said first power source, a base operatively connected to the drain of said P-channel MIS transistor and an emitter operatively connected to said output terminal.
 4. A logical gate circuit according to claim 2 or claim 3, wherein said output terminal is connected to an input terminal of a next stage gate, and the input terminal of the next stage gate provides a high input impedance.
 5. A logical gate circuit, comprising:a first power source for supplying a first level; a second power source for supplying a second level lower than the first level; an input terminal for receiving an input signal having one of the first and second levels; an output terminal for providing an output signal having one of the first and second levels; a PNP type bipolar transistor, having an emitter operatively connected to said first power source, having a collector operatively connected to said output terminal, and having a base, said output terminal outputting the output signal with the first level in response to said switching transistor having an ON state; an N-channel MIS transistor having a source operatively connected to said second power source, a drain operatively connected to said output terminal and a gate operatively connected to said input terminal, said N-channel MIS transistor being turned OFF in response to the input signal having the second level and being turned ON in response to the input signal having the first level, the output signal having the second level when said N-channel MIS transistor is ON; a first P-channel MIS transistor having a source operatively connected to the base of said PNP type bipolar transistor and a gate operatively connected to said output terminal, for controlling said PNP type bipolar transistor in response to the output signal, said second P-channel MIS transistor turning ON and OFF in response to the output signal having the second level and the first level, respectively; and a second P-channel MIS transistor having a source connected to the drain of said first P-channel MIS transistor, a gate operatively connected to said input terminal and a drain operatively connected to said second power source, for controlling said PNP: type bipolar transistor in response to the input signal, said second P-channel MIS transistor turning ON and OFF in response to the input signal having the second level and the first level, respectively, said PNP type bipolar transistor being turned ON only when said first and second P-channel MIS transistors are ON and provide a base current thereto.
 6. A logical gate circuit according to claim 5, wherein said active load circuit further comprises a PNP transistor having a collector operatively connected to said second power source, a base operatively connected to the drain of said N-channel MIS transistor and an emitter operatively connected to said output terminal.
 7. A logical gate circuit according to claim 5 or claim 6, wherein said output terminal is connected to an input terminal of a next stage gate, and the input terminal of the next stage gate provides a high input impedance.
 8. A logical gate circuit, operatively connected to first and second power sources, to supply an output signal at an output terminal in response to an input signal at an input terminal, the first power source having a level lower than the second power source, said logical gate circuit comprising:an NPN transistor and a PNP transistor, each having a collector connected to the output terminal, each having an emitter connected to the first and second power sources, respectively, and each having a base; first and second N-channel MIS transistor means connected in series between the base of said NPN transistor and the second power source; and first and second P-channel MIS transistor means connected in series between the base of said PNP transistor and the first power source, said first N-channel MIS transistor means and said first P-channel MIS transistor means having gates commonly connected to the output terminals turning ON and OFF in response to the output signal and said second N-channel MIS transistor means and said second P-channel MIS transistor means having gates commonly connected to the input terminal turning ON and OFF in response to the input signal.
 9. A logical gate circuit according to claim 1,wherein said active load circuit comprises a plurality of first enhancement-type transistors, connected in parallel between said first power source and said output terminal, and having gates operatively connected to the input terminal, wherein said input transistor means comprises a plurality of second enhancement-type transistors connected in series between said first power source and said control transistor means, and having gates operatively connected to said input terminal, and wherein the input signal has separate portions supplied by said input terminal to corresponding gates of said first and second enhancement-type transistors.
 10. A logical gate circuit according to claim 1,wherein said active load circuit comprises a plurality of first enhancement-type transistors, connected in series between said first power source and said output terminal, having gates operatively connected to said input terminal, wherein said input transistor means comprises a plurality of second enhancement-type transistors connected in parallel between said first power source and said control transistor means, having gates operatively connected to said input terminal, and wherein the input signal has separate portions supplied by said input terminal to corresponding gates of said first and second enhancement-type transistors. 